If Shī has appeared in your reading, the book is naming a moment when collective force must be brought to bear — not an isolated push, but an organised one. The character depicts a body of troops. The hexagram has only one yang line, in the second place, and the other five lines yield to it. One commander, many soldiers, a single cause.
Classical commentary places this hexagram immediately after Sòng, the conflict. The book is following a sequence: first the disagreement, then — if the disagreement cannot be resolved by discussion — the move to organised action. Shī does not celebrate this move. It examines its conditions.
What the book counsels is the joining of justification and competence. 丈人, the elder, the seasoned figure: only such a person can command without bringing disaster. The cause must be sound and the commander must be tested. The verdict 無咎 — without blame — is what is on offer when both conditions hold. Without them, even victory carries cost.
Shī's failure mode is the unjustified mobilisation: force assembled because it could be, not because it had to be. The hexagram appears when the reader is considering a large coordinated action. The book is asking the question the elder would ask first: is this the necessary fight, and am I the one to lead it?